This marks Trump's second direct attack on Amazon in less than a week. The president tweeted last week that Amazon was using the post office as its "delivery boy." He also said: "I have stated my concerns with Amazon long before the Election."

But some would argue Amazon has been good for the Postal Service. In fiscal 2017, the agency's revenue rose 12 percent after a poor financial performance for more than a decade.

This follows a report from Axios on Wednesday that said Trump was "obsessed" with going after Amazon and wanted to change the e-commerce giant's tax treatment. The report said that several of Trump's friends told him Amazon is hurting their businesses and "killing shopping malls and brick-and-mortar retailers."

Amazon shares lost more than 3 percent last week but are still up 23.8 percent year to date.